Electric-arc furnace dust (EAFD) is a waste by product material generated during steel making processes using EAF technology. 15-20 kg of the dust is generated per ton of steel product. The world generation of EAFD is estimated to be around 3.7 million tons per year. Further, with the continued increase in using EAF technology in worldwide steel production during the last decade, the problem of managing and handling EAFD is also increasing.
EAFD is collected in bag houses and it comes in the form of very fine powder. The chemical composition of EAFD varies according to the quality of steel scrap used in the manufacturing process. It is documented that the prevailing elements in the EAFD vary in concentration. However, the major elements found in EAFD are oxides of zinc and iron.
Concentration ranges of elements in EAFD are as follows:
ElementRange (%)Zn 2-46Fe10-45Ca 1-25Si1-5Al0.1-1.5Mg 1-12Na0.5-1.8K0.35-2.30Cd??Pb??
Two forms of particles are observed in EAFD using scanning electron microscope (SEM). The predominant spherical forms observed in EAFD were identified to include a mix of metal oxides (Fe, Zn, Mn, OFe2, O3). The minor angular-shaped particles were considered to be zincite (ZnO).
The x-ray diffraction (XRD) analysis of EAFD powder have shown the presence of magnetite (Fe2O3), Franklinite (ZnFe2O4), lime and zinc oxide (ZnO).
The mineralogical composition of EAFD shows that magnetite, lime, franklinite and zincite represent the major phases while magnezite, sylvite and hematite represent the minor ones.
One of the major problems encountered in the steel industry throughout the world is the management of the EAFDs which is listed as a hazardous waste by regulations in most developed countries. This listing is to a large extent due to the presence of leachable heavy metals. As such it cannot be disposed of directly as a landfill. Consequently, the problems associated with disposing of EAFD are sizable and costly.
Several routes for disposing of EAFD have been proposed in the literature. They include solidification/stabilization (S/S) technologies, recovery of zinc and lead and recycling and utilization of EAFD in cement and concrete manufacturing.
Even though S/S technologies that can be used to treat EAFD are improving they are the least desirable approach to manage the EAFD disposable because they offer no other benefits to the industry. The recovery method of zinc and lead have been developed and successfully applied especially to the EAFD that contain high percentages of zinc and lead. In some cases, this approach is not economically feasible, but still being used because it is the only viable option to manage the dust.
The concrete industry is one of the potential and energetic solutions used to consume waste materials. Accordingly, many researchers have investigated the incorporation of EAFD in concrete. It was observed that the concrete containing EAFD presented better mechanical behavior and improved durability performance when compared to a reference concrete mixture. However, the use of EAFD in concrete profoundly prolongs the setting time of concrete for up to 30 hours at low replacement levels of EAFD (less than 3%). This undesirable effect is considered as the main drawback of wider utilization of EAFD in concrete. The retardation of the setting time is attributed to the presence of heavy metals such as zinc and lead as they are present in a soluble form in their carrying minerals.
The current invention is proposed to eliminate the problem with extended setting time associated with the use of EAFD. This limits its use in concrete in a very small amount. This is achieved by bonding the heavy metals in EAFD in an insoluble crystalline phase with inherited cementitious properties. As a result, the detrimental effect of zinc and other heavy metals on setting time is eliminated. Thus, higher amounts of EAFD can be utilized in concrete without negatively affecting the fresh properties.
There are two prior art patents awarded to inventors at the King Saud University in Riyadh, Saudi Arabia. The first discloses the use of electric-arc furnace by product in concrete awarded to the following inventors, Faisal H. Al-Sugair; Abdulaziz I. Al-Negheimish; and Rajeh Z. Al-Zaid. As disclosed in that U.S. Pat. No. 5,557,031, an improved concrete or mortar material wherein cement is replaced by electric-arc furnace dust by amounts of from 0+% to 4% or more based on the amount of cement by weight. In addition, the electric-arc furnace dust can be used as an additive to obtain the same effect.
A more recent U.S. Pat. No. 8,152,917 of Abdulaziz I. Al-Negheimish; Rajeh Z. Al-Zaid and Abdulrahman M. Alhozaimy discloses a method for manufacturing concrete bodies or forms containing electric-arc furnace dust in the amount of up to about 4% at elevated temperatures to provide concrete bodies. The concrete bodies have improved compressive strength and slump retention capability. The method for producing the bodies includes the step of producing pre-selected amounts of electric-arc furnace dust, water, cement and aggregate. The electric-arc furnace dust is mixed with water and then added to the cement and aggregate and mixed together at a temperature of about 32° C. and 45° C. to form a hot mixture. The hot mixture is added to a mold and caste at an elevated temperature to form a body with improved strength and slump retention characteristics.